This invention relates to a method for producing whisker preforms and composites and more particularly to a method for producing Si.sub.3 N.sub.4 /SiAlON blend whisker preforms and composites.
The development of fiber reinforced composites has created a demand for reinforcement in the form of elongated, single-crystal fibers known as whiskers. Whiskers have been very popular in recent years as a reinforcement material for metal matrix composites (MMC) and ceramic matrix composites (CMC). The term whisker generally applies to any single-crystal fiber having a thickness less than 0.1 mm and a length to thickness ratio of at least 10:1.
Silicon nitride (S.sub.3 N.sub.4) is considered a highly desirable reinforcement material because of its high strength, wear-resistance, high decomposition temperature, oxidation resistance, excellent thermal shock properties, low coefficient of friction and resistance to corrosive environments. In addition, a material generally referred to by its acronym SiAlON (a solid solution consisting of silicon, aluminum, oxygen and nitrogen in a range of compositions) is also considered a desirable reinforcement material because of its high mechanical strength at room temperatures and above, high specific strength, hardness and toughness and low coefficient of friction and thermal expansion, and is also chemically inert and creep and oxidation resistance.
Major factors for selecting whiskers for reinforcing MMCs and CMCs are (1) compatibility of the interfacial bonding between matrices and whiskers, (2) geometrical factors of the whiskers such as shape, size and length/diameter (aspect) ratio, and (3) compatibility in physical properties such as thermal expansion coefficient of the matrix and reinforcing materials. By producing whiskers that are comprised of both Si.sub.3 N.sub.4 and SiAlON, (i.e., Si.sub.3 N.sub.4 at one end of the whisker and SiAlON at the other end), it is possible to provide a reinforcing material for a MMC or CMC utilizing the unique characteristics of both Si.sub.3 N.sub.4 and SiAlON whiskers.
It is an object of the present invention to provide a method for manufacturing Si.sub.3 N.sub.4 /SiAlON whisker preforms whereby the physical characteristics of the whisker can be manipulated through the controlled introduction of impurities into the manufacturing process.
It is another object of the present invention to provide a whisker preform having a unique composition of SiAlON at the nucleating end of the whisker and Si.sub.3 N.sub.4 at the other end of the whisker.
It is still another object of this invention to provide a method for manufacturing Si.sub.3 N.sub.4 /SiAlON whisker preforms and composites from readily available and low cost raw materials such as silicon carbide powder.
Additional objects, advantages and novel features of the invention will become apparent to those skilled in the art upon examination of the following and by practice of the invention.